Hiway Stabilizers pioneered the development of the Fill Conditioning process in New Zealand. The process enables fill materials (soils) which are significantly wet of optimum moisture content to be used instantly, thereby enabling earthworks operations to continue when conditions are unfavourable.

It is generally carried out in conjunction with earthworks operations where the material has very low strength due to its high moisture content and is unable to be handled or achieve structural requirements.  It is particularly well suited to sites with tight construction programmes, winter earthworks programmes or sites with limited drying area.

Conditioning Of Wet material The Easy Way

Fill Conditioning of wet material using lime is generally always more cost effective than cut to waste and importation of good quality fill material and also often cheaper than conventional earthworks drying techniques which are time consuming and rely on good weather conditions.

Fill Conditioning using lime provides immense benefits to the earthmoving contractor. By fill conditioning a wet ground after a wet weather episode, earthworks operations can continue immediately thereby limiting unproductive down time. The operation is very simple and enables large volumes of material to be dried instantly. Hiway Stabilizers plant is purpose built to handle almost any ground condition.  We have achieved in excess of 3,000m³ (solid) per day with one fill conditioning crew on past operations with ease.  This means that the earthworks contractor is able to cut to fill in excess of 3,000m³ (solid) per day without the constant threat of post test failures and rigorous supervision.

The Process

The process uses lime oxide as the conditioning agent.  The grade of lime oxide used is of very fine particle size to enable maximum coverage of the soil particles when mixed. 

The operation is carried out using specialised purpose built machinery.  This is usually of tracked configuration with very low ground pressure.  This plant is able to work on very soft and wet material and is designed to ensure controlled, accurate and consistent spread of additive and depth of mixing.  Other rubber tyred plant cannot deliver the same degree of precision as the tracked equipment as it has higher ground pressure and inevitably becomes stuck, slides or cannot maintain a consistent speed.  Hiway Stabilizers plant is capable of conditioning cut/fill layers up to 500mm depth.

The lime is delivered in pressurised tankers to site and pneumatically transferred from the tanker to the tracked spreader truck.  For sizeable contracts Hiway Stabilizers has a tanker and compressor to station on site to store material to further improve on site efficiency.

Once the lime oxide is received the material is applied at the prescribed rate.  This can be spread over almost any material or condition including puddles or silt traps.  The design application rate can be varied over a site depending on the variation in insitu and optimum moisture contents and the types of soils encountered.  Once spread the lime is then mixed into the wet material, without any slaking or watering, using a stabilising machine.  The lime is mixed into the soil material unslaked, as the intention is for the water within the soil to hydrate the lime.  This hydration process effectively dries back the wet material, producing a "mechanical" strength gain and is the key to the success of the whole operation.

As well as this "mechanical" strength gain there are also chemical strength gains as per the normal lime stabilisation process.  This chemical strength continues with time and can be particularly beneficial if the site requires haul roads or trenching work to be carried out at a later date.

Design / Testing

The design process for this operation should be approached pragmatically and does not usually require the same level of technical input as normal stabilisation.  Laboratory testing can be undertaken to confirm the natural strength of the material to be treated at its natural water content versus the strength achievable once dried back with the use of lime.

Due to varying on site soil types and moisture contents, this is usually not a practical procedure.  It should however, not be discounted as it provides a good guide in setting application rates. 

Designs usually allow for anywhere between 1% and 3% lime oxide to condition wet materials.  On rare occasions up to 5% lime oxide has been used.  Application rates will always vary for different material types and conditions.

The operation requires careful control throughout its implementation.  All spread rates are checked and recorded for each area of stabilisation completed.  The depth of conditioning is also checked and recorded. 

The performance of the treated material is of paramount importance and is usually controlled using traditional earthworks testing equipment which may consist of pilcon shear vane or scala penetrometer to test strength and nuclear densometer or core cutter to test compaction.

Summary

The fill conditioning process developed by Hiway Stabilizers has resulted in significant benefits to subdivision land developers where the completion of earthworks is critical to section sales and infrastructure projects where earthworks completion is critical to the civil works construction program.

Hiway Stabilizers are equipped to tackle the most demanding of sites achieving almost instantaneous results and high productions. Our specialist fill drying plant includes Komatsu CS360 tracked stabilising hoes, Mitsubishi LD1000 tracked spreader trucks, six wheel drive spreader truck and Komatsu BZ200 soil recyclers as well as our conventional stabilising hoes and spreaders which can be used where conditions allow.

The Fill Conditioning process provides a real and economic solution to an age old earthworks dilemma enabling projects to be completed on time when conditions would normally suggest otherwise.